XML Reference Guide

Mar 14, 2003

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One of the best things about open source is that if enough people want to do something, somebody's going to create a library to make it easy. Witness the Incutio PHP XML-RPC Library.

XML-RPC, as we've already discussed, is a type of simple Web service geared at telling a remote computer to do something, whether it's to return the current time or to add information to a database. The process involves sending XML files back and forth over an HTTP connection, so it can be accomplished in virtually any programming language on virtually any platform, but still, who wants to muck about creating and decoding XML, when it would be simpler to have a library handle that?

Today we're going to create a very simple identity verification service that uses the Incutio PHP XML-RPC Library for both the server and client. You can download the library at http://scripts.incutio.com/xmlrpc/.

Ultimately, the program will enable users to register a username and password, and will enable a site to check on a username/password combination. But we'll start by creating a very simple client that checks to see how many users are currently in the system. As you may recall, the XML message we're sending should look something like this:

<?xml version="1.0"?>

<methodCall>
   <methodName>ident.getUserCount</methodName>
   <params></params>
</methodCall>

This message tells the server to execute the function ident.getUserCount and return the results. The resulting XML looks something like this:

<?xml version="1.0"?>
<methodResponse>
   <params>
      <param>
         <value>
            <int>42</int>

         </value>
      </param>
   </params>
</methodResponse>

So let's start by creating a simple client to send the request:

<?php

include('IXR_Library.inc.php');

$client = new IXR_Client('http://www.nicholaschase.com/phpxmlrpc/server.php');

?>

First, we load the library, and then we instantiate the client class. From there, creating and sending the request is straightforward:

...
$client = new IXR_Client('http://www.nicholaschase.com/phpxmlrpc/server.php');
$client->query('ident.getUserCount');
print $client->getResponse();
...

The results, which are automatically converted to PHP data types by the library, should look something like this:

Sending parameters is pretty simple as well, accomplished by adding them to the query:

...
$client->query('ident.userExists', 'roadnick');
print $client->getResponse();
...

The result, depending on the username you send, is a Boolean value of true or false, which gets converted to a one or zero.

You can also pass multiple parameters as an array:

...
$params[0] = "roadnick";
$params[1] = "mypassword";
$client->query('ident.userLogin', $params);
print $client->getResponse();
...

In all of these cases, we have been dealing with and simple responses, but complex responses are handled just as easily, because they are returned to PHP as arrays.

Another time in which you are dealing with arrays is when the server returns an error. For example, if you try to create a username that already exists, the server will send back an error message:

...
$params[0] = "roadnick";
$params[1] = "mypassword";
$client->query('ident.createUser', $params);
print_r ($client->getResponse());
...

In this case, you can see the results of the print_r statement:

Array
(
    [faultCode] => -1
    [faultString] => Username roadnick already exists.
)

Of course, it would be much cleaner to deal with the errors within the code:

...
$params[0] = "roadnick";
$params[1] = "mypassword";
if (!$client->query('ident.createUser', $params)){
    die('Error: '.$client->getErrorCode()." -- ".$client->getErrorMessage());
} else {
   print_r ($client->getResponse());
}
...

Fortunately, the library is smart enough to determine that it is actually an error and not the typical response.

So that's the client side. It turns out the creating the server is also straightforward. The library supports the creation of the server as an object, but for those of you using PHP 4, you can also create it procedurally.

Start by creating the functions you want to serve:

<?php

include('IXR_Library.inc.php');

function getUserCount($args) {
    return 42;
}
function userExists($args) {
    if ($args == "roadnick"){
	return true;
    } else {
            return false;
    }
}
function userLogin($args){
    $username = $args[0];
    $password = $args[1];
    if ($username == 'roadnick' && $password == 'mypassword'){
        return "Valid login.";
    } else {
        return "Invalid login.  Please try again.";
    }
}
function createUser($args){
     $username = $args[0];
     $password = $args[1];
     if ($username == 'roadnick'){
        return new IXR_Error(-1, 'Username '.$username.' already exists.');
     } else {
        return "User created.";
     }
}
...

Obviously, these are placeholder functions for which the logic can be replaced later, after the server is up and running.

Now you can create the actual server by instantiating the IXR_Server class:

...    
        return "User created.";
     }

$functionMapping = array(
    'ident.getUserCount' => 'getUserCount',
    'ident.userExists' => 'userExists',
    'ident.userLogin' => 'userLogin',
    'ident.createUser' => 'createUser'
);
$server = new IXR_Server($functionMapping);

?>

The functionMapping array maps of the names you will pass any actual request to the functions to which they correspond. Finally, create the server.

As simple as this is, it is only a basic look at what you can do with the Incutio PHP XML-RPC Library. The library also enables you to process multiple calls in a single request and to create servers that will let a client know what methods are available, among other features.

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